Fishman Neo-Buster Humbucker Soundhole Acoustic Pickup & Feedback Buster Neodymium humbucking magnet structure for warm humbucking tone and exceptional string balanceIntegrated feedback-buster for high-volume playingLow profile, high impedance design needs no batteryFlexible surround reduces howling in high volume situationsEasy installation with no alteration fits most standard acoustic guitars with 3-7/8 or 4 diameter soundholeTool-free installation &nbsp;This humbucking magnetic soundhole pickup produces a warm and full sound while also greatly reducing hum&nbsp;and unwanted interference It also shares the same neodymium magnet structure as the award-winning Rare&nbsp;Earth pickup for exceptional string balance and incredible acoustic clarity Its low-profile, high impedance design needs no battery &nbsp;When you need to play in high-volume situations, the integrated soundhole cover reduces the build-up of energy inside the guitar that often leads to uncontrollable howling